1. Technical Field
The present disclosure relates in general to a processing system, and more particularly to determining an angle of incidence with respect to a workpiece processed in the processing system.
2. Background Art
Utilization of optical metrology in semiconductor manufacturing has grown significantly over the past several years. The technology provides capabilities to conduct measurements of a wide variety of critical device parameters, including, for example, critical dimensions, depths and sidewall angles. The benefits of optical metrology include non-invasive and fast measurement capabilities with relatively low cost of ownership. The non-contact characteristic of the optical metrology is of great value as any time a contact is made to the surface of a device there is a possibility that the device could be damaged and/or contaminated. For optical metrology tools to yield measurement results that match, it is necessary that the optical metrology tools produce well defined incident light beams, and properly collect reflected light beams for analysis.
One critical parameter for an optical metrology measurement is the angle of incidence (AOI) of the light beam. FIG. 1 shows an incident light beam 20 (incident beam) that strikes a target surface 22 at an angle 24 to a surface normal 26 perpendicular to target surface 22. Angle 24 is referred to as an “angle of incidence” (AOI). A plane 30 containing incident beam 20 and a reflected beam 32 is usually referred to as a plane of incidence. By definition, angle of incidence 24 equals ½ of an angle 34 between incidence beam 20 and reflected beam 32.
While the AOI of an optical metrology tool is usually defined by the manufacturer of the optical metrology tool, the actual AOI onto a wafer being measured may vary due to issues with the optical metrology tool and/or the wafer, such as, for example, the flatness and/or orientation of a chuck used to hold the wafer, or the condition of the wafer. In the case that the actual AOI is different than the defined AOI, the resultant measurement of the optical metrology tool will contain an error. The magnitude of the error depends on, inter alia, the magnitude of the difference between the actual AOI and the defined AOI.